U.S. patent number 10,661,273 [Application Number 15/293,134] was granted by the patent office on 2020-05-26 for two-dimensional micro- and nano-pattern, methods for forming the same, and microfluidic devices formed therefrom.
This patent grant is currently assigned to THE REGENTS OF THE UNIVERSITY OF MICHIGAN. The grantee listed for this patent is The Regents of the University of Michigan. Invention is credited to Long Chen, Lingjie J. Guo, Jong G. Ok, Ashwin Panday.
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United States Patent |
10,661,273 |
Ok , et al. |
May 26, 2020 |
Two-dimensional micro- and nano-pattern, methods for forming the
same, and microfluidic devices formed therefrom
Abstract
Methods of forming two-dimensional nanopatterns are provided.
The method may comprise periodically contacting a vibrating tool
comprising a patterned grating edge with a substrate along a first
direction in a grating-vibrational indentation patterning process.
The patterned grating edge defines a plurality of rows and a
plurality of interspersed troughs. The periodic contacting creates
a two dimensional array of discontinuous voids in a single-stroke
across the surface of the substrate. In other aspects, a
microfluidic device for selective arrangement of a microspecies or
nanospecies is provided, that includes a substrate comprising a
surface defining a two-dimensional pattern of microvoids or
nanovoids. In yet other aspects, the present disclosure provides a
method for selective arrangement of a microspecies or nanospecies
on a substrate.
Inventors: |
Ok; Jong G. (Seoul,
KR), Guo; Lingjie J. (Ann Arbor, MI), Chen;
Long (Ann Arbor, MI), Panday; Ashwin (Ann Arbor,
MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of Michigan |
Ann Arbor |
MI |
US |
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Assignee: |
THE REGENTS OF THE UNIVERSITY OF
MICHIGAN (Ann Arbor, MI)
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Family
ID: |
58499234 |
Appl.
No.: |
15/293,134 |
Filed: |
October 13, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170100716 A1 |
Apr 13, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62240975 |
Oct 13, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B81C
1/00031 (20130101); B01L 3/502761 (20130101); B01L
3/502707 (20130101); B81C 1/0046 (20130101); B01L
2300/0893 (20130101); B81B 2201/058 (20130101); B01L
2200/0668 (20130101); B01L 2400/0487 (20130101); B01L
2200/12 (20130101); B01L 2300/16 (20130101); B81B
2203/033 (20130101); B01L 2300/0877 (20130101) |
Current International
Class: |
B01L
3/00 (20060101); B81C 1/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Jong G. Ok. et al. Continuous and High-throughput Nanopatterning
Methodologies based on Mechanical Deformation. Journal of Materials
Chemistry C (2013) 1, 7681. cited by applicant .
Ahn, S. H. et al., "Dynamic nanoinscribing for continuous and
seamless metal and ploymer nanogratings," Nano Lett. 9, 4392-4397
(2009). cited by applicant .
Ahn, S. H. et al. "Spontaneous Formation of Periodic Nanostructures
by Localized Dynamic Wrinkling," Nano Lett. 9, 4392-4397 (2009).
cited by applicant .
Ok, J. G. et al, "Continuous fabrication of scalable 2-dimensional
(2D) micro- and nanostructures by sequential 1D mechanical
patterning process," Nanoscal 5, 4636-42 (2014). cited by applicant
.
Ahn, S. H. et al., "Large-Area Roll-to-Roll and Roll-to-Plate
Nanoimprint Lithography: A Step toward High-Throughput Application
of Continuous Nanoimprinting," ACSNANO 3, No. 8, 2304-2310 (2009).
cited by applicant .
Ashwin Panday, et al. Size Selective Nanoparticle Confinement in 2D
Nanovoid Array in Aqueous Solution. 18th International Conference
on Miniaturized Systems for Chemistry and Life Sciences. Oct.
26-30, 2014, San Antonio, Texas. pp. 1865-1867. cited by
applicant.
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Primary Examiner: Ayub; Hina F
Assistant Examiner: Merlino; Amanda
Attorney, Agent or Firm: Harness, Dickey & Pierce,
P.L.C.
Government Interests
GOVERNMENT SUPPORT
This invention was made with government support under DMR-1120187
awarded by the National Science Foundation. The Government has
certain rights in the invention.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 62/240,975, filed on Oct. 13, 2015. The entire disclosure of
the above application is incorporated herein by reference.
Claims
What is claimed is:
1. A microfluidic device for selective arrangement of at least one
of a microspecies and nanospecies, the device comprising: a
substrate comprising a surface defining a two-dimensional
sinusoidal pattern of discontinuous microvoids or nanovoids each
comprising at least one curved surface; a microfluidic compartment,
wherein the substrate is disposed within the compartment and the
surface contacts a fluid comprising the at least one of the
microspecies and nanospecies contained in the microfluidic
compartment; an inlet to the microfluidic compartment; and an
outlet to the microfluidic compartment; wherein the fluid
comprising the at least one of the microspecies and nanospecies is
introduced to the microfluidic compartment via the inlet and exits
the microfluidic compartment via the outlet.
2. The microfluidic device of claim 1, wherein the substrate is a
polymeric substrate selected from the group consisting of:
polyethylene terephthalate (PET), polycarbonate (PC), phenol
formaldehyde resins (PF), and perfluoroalkoxy (PFA).
3. The microfluidic device of claim 1, wherein the microfluidic
compartment comprises at least one transparent region through which
the surface of the substrate is visible to an external
detector.
4. The microfluidic device of claim 1, wherein the two-dimensional
pattern of nanovoids is a sinusoidal pattern of nanovoids having a
period of greater than or equal to about 50 nm to less than or
equal to about 1 .mu.m.
5. The microfluidic device of claim 1, wherein the surface has a
first charge and the microspecies and nanospecies has a second
charge opposite charge to the first charge, so that the surface
attracts the microspecies and nanospecies.
6. The microfluidic device of claim 1, wherein the surface
comprises a coating having a first charge and the microspecies and
nanospecies has a second charge opposite charge to the first
charge, so that the surface attracts the microspecies and
nanospecies.
7. The microfluidic device of claim 6, wherein the coating
comprises aluminum oxide (Al.sub.2O.sub.3) having a positive charge
and the at least one of the microspecies and nanospecies has a
negative charge.
8. A method of forming the substrate comprising the surface
defining the two-dimensional sinusoidal pattern of discontinuous
microvoids or nanovoids for the microfluidic device of claim 1, the
method comprising: periodically contacting a vibrating tool
comprising a patterned grating edge with the substrate along a
first direction in a grating-vibrational indentation patterning
process, wherein the patterned grating edge defines a plurality of
rows and a plurality of interspersed troughs and the periodically
contacting creates a two dimensional array of discontinuous voids
in a single-stroke across the substrate to form the two-dimensional
sinusoidal pattern of discontinuous microvoids or nanovoids.
9. The method of claim 8, wherein the vibrating tool is a cleaved
hard mold tool comprising silicon dioxide (SiO.sub.2).
10. The method of claim 8, wherein the plurality of rows defines a
period of greater than or equal to about 50 nm to less than or
equal to about 10 .mu.m.
11. The method of claim 8, wherein the substrate is a polymeric
substrate selected from the group consisting of: polyethylene
terephthalate (PET), polycarbonate (PC), phenol formaldehyde resins
(PF), and perfluoroalkoxy (PFA).
12. A method for selective arrangement of at least one of a
microspecies and nanospecies on a substrate, the method comprising:
passing a fluid comprising the at least one of the microspecies and
nanospecies over a surface of the substrate comprising a
two-dimensional sinusoidal pattern of discontinuous microvoids or
nanovoids each comprising at least one curved surface, wherein the
at least one of the microspecies and nanospecies has a first charge
and the surface has a second charge opposite to the first charge,
wherein at least a portion of the at least one of the microspecies
and nanospecies in the fluid is trapped and assembled within the
two-dimensional sinusoidal pattern of discontinuous microvoids or
nanovoids.
13. The method of claim 12, wherein the at least one of the
microspecies and nanospecies is a charged biological species or a
charged nanoparticle.
14. The method of claim 13, wherein the charged biological species
is selected from the group consisting of: proteins, peptides,
nucleic acids, cells, viruses, bacteria, and combinations
thereof.
15. The method of claim 12, wherein each void of the
two-dimensional sinusoidal pattern of discontinuous microvoids or
nanovoids has a hemispherical shape.
16. The method of claim 12, wherein the fluid is introduced into an
inlet of a microfluidic compartment in which the substrate is
disposed, so that the fluid flows over the surface of the polymeric
substrate comprising the two-dimensional sinusoidal pattern of
discontinuous microvoids or nanovoids in the compartment, wherein
after at least a portion of the at least one of the microspecies
and nanospecies in the fluid is trapped and assembled within the
two-dimensional sinusoidal pattern of discontinuous microvoids or
nanovoids, the remaining fluid passes out an exit of the
microfluidic compartment.
17. A microfluidic device for selective arrangement of a
nanospecies, the device comprising: a substrate comprising a
surface defining a two-dimensional pattern of nanovoids comprising
at least one curved surface and having a maximum dimension of less
than or equal to about 1 .mu.m; a microfluidic compartment, wherein
the substrate is disposed within the compartment and the surface
contacts a fluid comprising the nanospecies contained in the
microfluidic compartment; an inlet to the microfluidic compartment;
and an outlet to the microfluidic compartment; wherein the fluid
comprising the nanospecies is introduced to the microfluidic
compartment via the inlet and exits the microfluidic compartment
via the outlet.
18. The microfluidic device of claim 17, wherein the
two-dimensional pattern of nanovoids is a sinusoidal pattern of
nanovoids having a period of greater than or equal to about 50 nm
to less than or equal to about 1 .mu.m, wherein each of the
nanovoids has a hemispherical shape.
19. The microfluidic device of claim 17, wherein the surface
comprises a coating comprising aluminum oxide (Al.sub.2O.sub.3)
having a positive charge and the at least one of the microspecies
and nanospecies has a negative charge.
Description
FIELD
The present disclosure relates to methods for fabricating
continuous and scalable multidimensional (e.g., two-dimensional
(2D)) micro/nano-scale structures via a "single-stroke" 2D
patterning using a grating tool with a vibrational indentation
patterning (VIP) (Grating-VIP; G-VIP) and microfluidic devices
incorporating such 2D micro/nano-scale structures for selective
arrangement of nanospecies.
BACKGROUND
This section provides background information related to the present
disclosure which is not necessarily prior art. Two-dimensional
micro-patterning is more useful for manufacturing thin film
structures and a variety of devices compared to vertically stacked
one-dimensional array or three-dimensional composite structures.
This planar two-dimensional nanopatterning has been used widely for
various functional films such as anti-reflective coating, plasmonic
surface, filters, bio-engineering template, etc. and applied to a
variety of thin film devices, such as light source, organic
optoelectronic devices, photovoltaic cells, etc, for improved
performance. The two-dimensional micro-pattern is typically formed
by using technologies such as laser interference lithography that
involves reactive ion etching and electron beam lithography.
However, these technologies have limit on the size of the pattern
that can be formed, have low productivity and are expensive.
SUMMARY
This section provides a general summary of the disclosure, and is
not a comprehensive disclosure of its full scope or all of its
features.
In certain aspects, the present disclosure provides a method of
forming a two-dimensional pattern on a substrate. The method may
comprise periodically contacting a vibrating tool comprising a
patterned grating edge with a substrate along a first direction in
a grating-vibrational indentation patterning process. The patterned
grating edge defines a plurality of rows and a plurality of
interspersed troughs. The periodic contacting creates a two
dimensional array of discontinuous voids in a single-stroke across
the surface of the substrate.
In other aspects, the present disclosure provides a microfluidic
device for selective arrangement of a microspecies and nanospecies.
The microfluidic device comprises a substrate comprising a surface
defining a two-dimensional pattern of microvoids or nanovoids. The
microfluidic device includes a microfluidic compartment. The
substrate is disposed within the microfluidic compartment and the
surface contacts a fluid comprising the microspecies and
nanospecies contained in the microfluidic compartment. The
microfluidic device also includes an inlet and an outlet to the
microfluidic compartment; where the fluid comprising the
microspecies and nanospecies is introduced to the microfluidic
compartment via the inlet and exits the microfluidic compartment
via the outlet.
In yet other aspects, the present disclosure provides a method for
selective arrangement of a microspecies and nanospecies on a
substrate. The method comprises passing a fluid comprising a
microspecies and nanospecies over a surface of the substrate
comprising a two-dimensional pattern of microvoids or nanovoids.
The fluid may be an ionic fluid. The microspecies and nanospecies
have a first charge and the surface has a second charge opposite to
the first charge. At least a portion of the microspecies and
nanospecies in the fluid is trapped and assembled within the
two-dimensional pattern of microvoids or nanovoids.
Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
The drawings described herein are for illustrative purposes only of
selected embodiments and not all possible implementations, and are
not intended to limit the scope of the present disclosure.
FIG. 1 shows a two-dimensional nanopattern formed with a dynamic
nanoinscribing (DNI) technique in accordance with certain aspects
of the present disclosure.
FIGS. 2A-2B. FIG. 2A shows a two-dimensional nanopattern formed
with a vibrational indentation patterning (VIP) technique in
accordance with certain other aspects of the present disclosure.
FIG. 2B is a schematic depicting the overall VIP process where the
vertically vibrating tool edge periodically or intermittently
indents the line patterns on a linearly moving substrate.
FIG. 3 shows a two-dimensional nanopattern formed with a single
step combined grating-vibrational indentation patterning (G-VIP)
technique in accordance with yet other aspects of the present
disclosure.
FIGS. 4A-4D show two-dimensional nanopatterns formed in accordance
with certain aspects of the present disclosure. FIG. 4A shows a
dynamic nanoinscribing (DNI)-DNI grating, FIG. 4B shows a
vibrational indentation patterning (VIP)-VIP grating, FIG. 4C shows
a DNI-VIP grating, and FIG. 4D shows a VIP-DNI grating.
FIGS. 5A-5D show SEM images of two-dimensional nanopatterns formed
with the dynamic nanoinscribing in accordance with certain aspects
of the present disclosure, including magnified side views in each
inset. The grating in FIG. 5A is formed via dynamic nanoinscribing
on a perfluoroalkoxy (PFA) substrate at 80.degree. C. and with 5N
of applied force and has a depth of 350 nm. FIG. 5B shows a
polycarbonate (PC) substrate dynamically inscribed at 80.degree. C.
with 5N of applied force and a depth of 180 nm. FIG. 5C shows a PC
substrate dynamically inscribed at 120.degree. C. and 5N of applied
force with a depth of 200 nm. FIG. 5D shows a PC substrate
dynamically inscribed at 80.degree. C. and 1N of applied force with
a depth of 130 nm. Scale bars are 1 .mu.m.
FIGS. 6A-6D show SEM images of two-dimensional nanopatterns formed
with the vibrational indentation patterning in accordance with
certain aspects of the present disclosure. Schematic illustrations
over the SEM images show patterning sequences. FIG. 6A shows a
two-dimensional vibrational indentation patterning at a 45.degree.
tilted view on polyethylene terephthalate (PET), where a first
direction of VIP is a shallow pass with relatively low applied
pressure, while a second orthogonal direction is a deeper pass with
greater applied pressure. Scale bar is 10 .mu.m. The inset of FIG.
6A shows a detailed view with a scale bar of 2 .mu.m. FIG. 6B shows
two-dimensional patterning on polycarbonate (PC), where the first
direction of patterning is done by dynamic inscribing (DNI) and the
second orthogonal direction of patterning is done by vibrational
indentation patterning (VIP). Scale bar is 5 FIG. 6C is a top view
of two-dimensional patterning under different conditions on PC,
where the first direction of patterning is done by vibrational
indentation patterning (VIP) and the second orthogonal direction of
patterning is done by dynamic inscribing (DNI). A deep
high-frequency VIP followed by a shallow DNI step is shown in FIG.
6C, while the inset shows an SEM of a two-dimensional pattern
formed by a shallow, high-frequency VIP step followed by a shallow
DNI step. Scale bars are 5 .mu.m. FIG. 6D is a top view of
two-dimensional patterning, where the first direction of patterning
is done by a shallow, low-frequency, vibrational indentation
patterning (VIP) followed by the second orthogonal direction of
patterning of deep dynamic inscribing (DNI). Scale bar is 5 .mu.m.
All VIP processing temperatures for forming the patterns are at
room temperature and all DNI processing temperatures are at
120.degree. C.
FIGS. 7A-7B show SEM images of two-dimensional nanopatterns formed
with the grating-vibrational indentation patterning (G-VIP)
techniques where a grating mold edge makes periodical indentations
over the moving substrate to realize two-dimensional patterns in
one stroke according to certain aspects of the present disclosure.
FIG. 7A shows a G-VIP patterned polycarbonate (PC) substrate, while
FIG. 7B shows a G-VIP perfluoroalkyl (PFA) substrate with
directions marked. Scale bars are 5 .mu.m.
FIGS. 8A-8D. FIG. 8A shows a two-dimensional nanopattern having a
700 nm period void pattern formed with a dynamic nanoinscribing
(DNI)-DNI pattern on a polycarbonate (PC) substrate in accordance
with certain aspects of the present disclosure. FIG. 8B shows a
schematic of a top view and side view of a fluidic cell chamber
including a substrate patterned in accordance with certain aspects
of the present disclosure. The microfluidic cell contains a
two-dimensional DNI-DNI pattern like that in FIG. 8A coated with a
10 nm thick Al.sub.2O.sub.3 coating. A suspension of nanoparticles
(e.g., polystyrene nanoparticles) is injected into the cell
immersed in a solution (e.g., NaCl solution), while a microscope
monitors and records the motion of the NPs. FIG. 8C shows
epifluorescence microscopic images of nanoparticles (e.g.,
polystyrene nanoparticles) docked in the Al.sub.2O.sub.3-coated
two-dimensional DNI-DNI framework (scale is 10 .mu.m). The inset in
FIG. 8C shows SEM images taken after the sample is dried, where the
enlarged view in the lower-right corner shows three nanoparticles
confined in three grooves in series (scale is 5 .mu.m). FIG. 8D
shows simulation characteristics as a nanoparticle descends in the
z-direction into the nanovoid of a patterned surface prepared in
accordance with certain aspects of the present disclosure.
FIGS. 9A-9E. FIG. 9A is a schematic illustration of a dynamic
nano-inscribing (DNI) process for a single-stroke one dimensional
(1D) nanopatterning or two-dimensional (2D) nanopatterning by
sequential combination. A well-cleaved edge of a 700 nm-period
nanograting mold formed of SiO.sub.2 is used to create the
nanopattern. FIG. 9B shows an SEM image of a side view of the
patterned surface of the nanograting mold with the 700 nm period
grating. FIG. 9C shows a continuously-created 1D grating formed
after the nanograting mold contacts and slides over a polymeric
substrate under a conformal contact and localized heating. FIG. 9D
shows a 2D nanovoid pattern formed from a nanograting mold (scale
bar 1 .mu.m). FIG. 9D shows well-defined sinusoidal surface
profiles (scale bar 1 .mu.m). FIG. 9E is a perspective view of an
SEM of 2D-DNI-fabricated nanovoid arrays.
FIGS. 10A-10D. FIGS. 10A-10C show particle directed assembly
including an epi-fluorescent micrograph of 500 nm diameter
particles assembling on: an unpatterned, uncoated polycarbonate
substrate (FIG. 10A), an unpatterned, 10 nm Al.sub.2O.sub.3 coated
polycarbonate substrate (FIG. 10B), and a patterned substrate
coated with 10 nm Al.sub.2O.sub.3 (FIG. 10C). The inset in FIG. 10C
charts zoom-in microscopy and SEM images of the trapped
nanoparticles. FIG. 10D shows a nanovoid fill ratio as a function
of the particle concentration. The diameter of the particles is 500
nm.
FIGS. 11A-11F. Size-selected trapping of nanoparticles on patterned
surfaces formed in accordance with certain aspects of the present
disclosure are shown. Microscope and SEM images of the
nanoparticles trapped to the patterned structure for 200 nm
particles (FIGS. 11A and 11D), 500 nm particles (FIGS. 11B and
11E), 1 .mu.m particles (FIGS. 11C and 11F). The inset picture in
FIG. 11B shows the zoomed-in view of the trapped particles.
FIGS. 12A-12F. Energy profiles of the traps are shown. In FIGS.
12A-12C, the geometry of the particles at the lowest positions in
the voids for 200 nm (FIG. 12A), 500 nm (FIG. 12B), and 1 .mu.m
(FIG. 12C) particles are shown, respectively. FIGS. 12D-12F show
calculated energy change of the system, when particles are
approaching the bottom of the void in z-direction for 200 nm (FIG.
12D), 500 nm (FIG. 12E) and 1 .mu.m (FIG. 12F) diameter particles
respectively.
FIGS. 13A-13B. Size-selectivity is explored. FIG. 13A shows a depth
of the free energy potential well for nanoparticles particles in
nanovoids having different sizes. The insets show the geometry of
the nanovoids and particles at the lowest positions in the voids.
FIG. 13B shows electric double layers (EDLs) of overlapping areas
for particles in the voids with different sizes. The insets show
the schematics of EDLs overlapping when particles are located at
the lowest positions in the voids for 200 nm, 500 nm and 1 .mu.m
particles. Only particles with particular sizes fitting the void
geometry well can obtain largest EDLs overlapping areas.
Corresponding reference numerals indicate corresponding parts
throughout the several views of the drawings.
DETAILED DESCRIPTION
Example embodiments are provided so that this disclosure will be
thorough, and will fully convey the scope to those who are skilled
in the art. Numerous specific details are set forth such as
examples of specific compositions, components, devices, and
methods, to provide a thorough understanding of embodiments of the
present disclosure. It will be apparent to those skilled in the art
that specific details need not be employed, that example
embodiments may be embodied in many different forms and that
neither should be construed to limit the scope of the disclosure.
In some example embodiments, well-known processes, well-known
device structures, and well-known technologies are not described in
detail.
The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting. As used herein, the singular forms "a," "an," and "the"
may be intended to include the plural forms as well, unless the
context clearly indicates otherwise. The terms "comprises,"
"comprising," "including," and "having," are inclusive and
therefore specify the presence of stated features, elements,
compositions, steps, integers, operations, and/or components, but
do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof. Although the open-ended term "comprising," is to be
understood as a non-restrictive term used to describe and claim
various embodiments set forth herein, in certain aspects, the term
may alternatively be understood to instead be a more limiting and
restrictive term, such as "consisting of" or "consisting
essentially of" Thus, for any given embodiment reciting
compositions, materials, components, elements, features, integers,
operations, and/or process steps, the present disclosure also
specifically includes embodiments consisting of, or consisting
essentially of, such recited compositions, materials, components,
elements, features, integers, operations, and/or process steps. In
the case of "consisting of," the alternative embodiment excludes
any additional compositions, materials, components, elements,
features, integers, operations, and/or process steps, while in the
case of "consisting essentially of" any additional compositions,
materials, components, elements, features, integers, operations,
and/or process steps that materially affect the basic and novel
characteristics are excluded from such an embodiment, but any
compositions, materials, components, elements, features, integers,
operations, and/or process steps that do not materially affect the
basic and novel characteristics can be included in the
embodiment.
Any method steps, processes, and operations described herein are
not to be construed as necessarily requiring their performance in
the particular order discussed or illustrated, unless specifically
identified as an order of performance. It is also to be understood
that additional or alternative steps may be employed, unless
otherwise indicated.
When a component, element, or layer is referred to as being "on,"
"engaged to," "connected to," or "coupled to" another element or
layer, it may be directly on, engaged, connected or coupled to the
other component, element, or layer, or intervening elements or
layers may be present. In contrast, when an element is referred to
as being "directly on," "directly engaged to," "directly connected
to," or "directly coupled to" another element or layer, there may
be no intervening elements or layers present. Other words used to
describe the relationship between elements should be interpreted in
a like fashion (e.g., "between" versus "directly between,"
"adjacent" versus "directly adjacent," etc.). As used herein, the
term "and/or" includes any and all combinations of one or more of
the associated listed items.
Although the terms first, second, third, etc. may be used herein to
describe various steps, elements, components, regions, layers
and/or sections, these steps, elements, components, regions, layers
and/or sections should not be limited by these terms, unless
otherwise indicated. These terms may be only used to distinguish
one step, element, component, region, layer or section from another
step, element, component, region, layer or section. Terms such as
"first," "second," and other numerical terms when used herein do
not imply a sequence or order unless clearly indicated by the
context. Thus, a first step, element, component, region, layer or
section discussed below could be termed a second step, element,
component, region, layer or section without departing from the
teachings of the example embodiments.
Spatially or temporally relative terms, such as "before," "after,"
"inner," "outer," "beneath," "below," "lower," "above," "upper,"
and the like, may be used herein for ease of description to
describe one element or feature's relationship to another
element(s) or feature(s) as illustrated in the figures. Spatially
or temporally relative terms may be intended to encompass different
orientations of the device or system in use or operation in
addition to the orientation depicted in the figures.
The size of the elements or the relative size between the element
or elements in the figures may be shown to be exaggerated for more
clear understanding of the invention. In addition, the shape of the
elements shown in the figures may be somewhat changed by the
variation of the manufacturing process or the like. Accordingly,
the embodiments described herein and should not be limited to the
shape shown in the drawings unless otherwise stated, it shall be
understood to include a certain amount of variation.
Throughout this disclosure, the numerical values represent
approximate measures or limits to ranges to encompass minor
deviations from the given values and embodiments having about the
value mentioned as well as those having exactly the value
mentioned. Other than in the working examples provided at the end
of the detailed description, all numerical values of parameters
(e.g., of quantities or conditions) in this specification,
including the appended claims, are to be understood as being
modified in all instances by the term "about" whether or not
"about" actually appears before the numerical value. "About"
indicates that the stated numerical value allows some slight
imprecision (with some approach to exactness in the value;
approximately or reasonably close to the value; nearly). If the
imprecision provided by "about" is not otherwise understood in the
art with this ordinary meaning, then "about" as used herein
indicates at least variations that may arise from ordinary methods
of measuring and using such parameters. For example, "about" may
comprise a variation of less than or equal to 5%, optionally less
than or equal to 4%, optionally less than or equal to 3%,
optionally less than or equal to 2%, optionally less than or equal
to 1%, optionally less than or equal to 0.5%, and in certain
aspects, optionally less than or equal to 0.1%.
In addition, disclosure of ranges includes disclosure of all values
and further divided ranges within the entire range, including
endpoints and sub-ranges given for the ranges.
Example embodiments will now be described more fully with reference
to the accompanying drawings.
Beyond uniaxial nanostructures, such as nanogratings or
one-dimensional (1D) nanomaterials (e.g., nanowires and nanotubes),
multi-dimensional nanoarchitectures integrating micro/nano-scale
features are desirable and their application has permeated into
many interdisciplinary fields.
Continuous mechanical nanopatterning methods, such as dynamic
nanoinscribing (DNI) and vibrational indentation patterning (VIP),
roll-to-roll nanoimprinting (R2RNIL), and localized dynamic
wrinkling (LDW) enable the continuous and high-speed fabrication of
micro/nano-grating patterns with simple setups and without the need
for intricate masks; DNI inscribes, VIP indents, R2RNIL imprints
micro/nano-scale grating patterns very easily on flexible
substrates.
In certain aspects, the present disclosure provides a unique
combination of these patterning techniques, a new process is
provided for the continuous and scalable "direct-writing" of
two-dimensional (2D) micro/nano-patterns. The present disclosure
also contemplates is a "single-stroke" 2D patterning by adapting
the grating-containing DNI tool as a vibrating edge in the VIP
process. Because both DNI and VIP are fully capable of period
control, a variety of large-area 2D patterns of desired dimensions
can be continuously written on any substrates softer than the
writing tool. In certain aspects, the present disclosure provides
new 2D patterns of arrays of microvoids or nanovoids, including
sinusoidal microvoid or nanovoid patterns. Further, microfluidic
devices incorporating substrates having such 2D patterns are
provided that can enable size selective separation and assembly of
nanomaterials and colloidal materials, such as nanoparticles,
cells, and the like.
Thus, the present disclosure contemplates scalable fabrication of
multidimensional nanopatterns via sequential combination of
continuous one-dimensional nanopatterning strokes. A versatile and
simple methodology is thus provided for continuous and scalable 2D
micro/nano-structure fabrication via sequential 1D patterning
strokes enabled by dynamic nano-inscribing (DNI) and vibrational
indentation patterning (VIP) as well as a "single-stroke" 2D
patterning using a new tool that has a patterned grating edge
enabling a new grating-vibrational indentation patterning process
(G-VIP). Various applications requiring 2D micro/nano-patterns with
good scalability and reproducibility can make use of this
technique.
In certain aspects, a method of forming the two-dimensional
nanopatterns includes a step to form a pattern on the substrate
using at least one process selected from dynamic nanoinscribing
using a first mold and vibrational indentation patterning using a
second mold.
The term dynamic nanoinscribing used herein means method of forming
a pattern by continuously contacting an edge of a mold or tool with
a moving substrate. Vibrational indentation patterning means a
method of forming a pattern by vertically vibrating an edge of a
mold or tool and only periodically contacting the edge with a
moving substrate as it passes by.
FIG. 1 shows micro-patterning using dynamic nanoinscribing. As
shown in FIG. 1, the dynamic nanoinscribing (Dynamic Nano
Inscribing, DNI) uses a sharp edge of a hard grating mold or tool
to inscribe a pattern onto a polymer substrate by plastically
deforming it. The mold edge can be locally heated to control the
degree of plastic deformation of the substrate at contact, thereby
tailoring the resulting pattern geometry. The mold or tool may have
a patterned contact surface that defines a plurality of distinct
rows (or peaks) and a plurality of troughs (or valleys)
interspersed therebetween. The pattern may thus define multiple
separate distinct lines.
The substrate may be a polymeric substrate. In certain aspects, the
substrate may be a polymeric substrate selected from the group
consisting of: polyethylene terephthalate (PET), polycarbonate
(PC), phenol formaldehyde resins (PF), perfluoroalkoxy (PFA), and
combinations thereof. However, other substrates that are softer
than the mold tool and undergo plastic deformation are also
contemplated and may be used.
The mold tools may be formed from fabricated polymer patterns that
are transferred onto silicon (Si) wafers using UV-curable
epoxysilicone resin.
The dynamic nanoinscribing can form a line type pattern by bringing
the mold edge in contact with the substrate at a predetermined
angle. A slight normal force and local heating can be applied to
the mold tool if necessary, and then the mold edge is slid over the
substrate in a first direction while the conformal contact is
maintained.
As a result, the pattern is continuously inscribed on a substrate
without seams until the process ends. The dynamic nanoinscribing
enables indefinite large area patterning irrespective of the mold
area. Mesh patterns can be formed by performing two dynamic
nanoinscribing processes in series along two different directions
at an angle to one another, for example, along orthogonal
directions with a 90.degree. angle in between.
FIGS. 2A-2B show micro-patterning using vibrational indentation
patterning in accordance with other aspects of the present
disclosure. As shown in FIG. 2A, the vibrational indentation
patterning (Vibrational Indentation Patterning, VIP) utilizes
vertical vibration of a flat, continuous, sharp edge of a rigid
tool, which makes periodic indentations onto a moving substrate
with a controlled gap from the tool. FIG. 2B shows the overall VIP
process where the vertically vibrating flat tool edge periodically
(or intermittently) indents line patterns on a linearly moving
substrate beneath the tool edge. The controlled vibration is
generated by operating a high-speed servo motor with a mass
eccentrically mounted on the spindle head. The tool is arranged in
a tool holder that is disposed at an angle (.THETA.) with respect
to the linear substrate. A direction of the substrate as it is fed
into the device is shown along with a velocity (V). The frequency
(f) of the vibration impacts the periodicity of the spacing between
indentations (shown as wavelength--.lamda.), as does the substrate
velocity (V) of the passing substrate. Thus, a period is generally
the interval/distance between a first feature and a second feature
in the same pattern. The period control in VIP is possible simply
by adjusting the vibration frequency and/or substrate moving speed.
The pattern may form a plurality of parallel and spaced apart
lines. As noted above, the polymer substrate may include
polyethylene terephthalate (PET), polycarbonate (PC), phenol
formaldehyde resins (PF), and/and perfluoroalkoxy (PFA), by way of
example. The fabricated polymer patterns may be transferred onto
silicon (Si) wafers using UV-curable epoxysilicone resin.
The vibrational indentation patterning can be an even more
economical process than the dynamic nanoinscribing as it uses
simple molds with a flat edge. By vertically vibrating a flat,
sharply-cleaved mold (e.g., formed of Si.sub.3N.sub.4) tilted at
the desired angle (e.g., 45.degree.) over a horizontally-moving
substrate with lesser hardness, periodic gratings or lines with
arbitrary spacing can be "indented" in a continuous manner. Mesh
patterns or gratings with intersecting lines can be formed by
performing two vibrational indentation patterning processes with
same frequency and force in series along two different directions,
for example, along orthogonal directions.
The two-dimensional pattern may be formed by dynamic
nanoinscribing, so that morphology of the pattern can be controlled
by controlling the force applied to the substrate and the mold or
tool and the temperature of the edge of the mold or tool in contact
with the substrate.
The two-dimensional pattern may also be formed by vibrational
indentation patterning, so that morphology of the pattern can be
controlled by controlling the vibration frequency and amplitude of
the mold or tool, the moving speed of the substrate and the gap
between the mold or tool and the substrate.
Where the 2D pattern is formed by the vibrational indentation
patterning, the VIP mold or tool may have multiple edges that are
spaced apart from each other, as will be described further
below.
FIGS. 4A-4D shows examples of two-dimensional micro-patterning
according to certain aspects of the present disclosure. As shown in
FIGS. 4A-4D, various forms of two-dimensional nanopatterns can be
formed by performing dynamic nanoinscribing and vibrational
indentation patterning steps twice in different directions. Various
forms of two-dimensional nanopatterns can be formed by performing
one of the dynamic nanoinscribing or the vibrational indentation
patterning in the first direction relative to the polymer
substrate, and performing one of the dynamic nanoinscribing or the
vibrational indentation patterning in the second direction relative
to the polymer substrate, orthogonal to the first direction.
The step of forming the 2D pattern may include, forming a first
pattern by performing one of the dynamic nanoinscribing or the
vibrational indentation patterning in a first direction relative to
the substrate, and forming a second pattern by performing one of
the dynamic nanoinscribing or the vibrational indentation
patterning in a second direction at an angle with respect to the
first direction. In certain aspects, the first direction may be at
an angle of 90.degree. to the second direction and therefore the
directions are orthogonal to one another.
As shown in FIG. 4A, forming the pattern may include forming a
first pattern 20 by performing dynamic nanoinscribing (DNI) in a
first direction relative to the substrate, and forming a second
pattern 22 by performing dynamic nanoinscribing in a second
direction disposed at an angle to the first direction. In certain
aspects, the first direction may be at an angle of 90.degree. to
the second direction and therefore the directions are orthogonal to
one another.
As shown in FIG. 4B, forming the pattern may include forming a
first pattern 24 by performing vibrational indentation patterning
in the first direction relative to the substrate, and forming
second pattern 26 by performing vibrational indentation patterning
in the second direction at an angle to the first direction. In
certain aspects, the first direction may be at an angle of
90.degree. to the second direction and therefore the directions are
orthogonal to one another.
As shown in FIG. 4C, forming the pattern may also include forming a
first pattern 28 by performing dynamic nanoinscribing in a first
direction relative to the substrate, and forming a second pattern
30 by performing vibrational indentation patterning in the second
direction at an angle to the first direction. In certain aspects,
the first direction may be at an angle of 90.degree. to the second
direction and therefore the directions are orthogonal to one
another.
As shown in FIG. 4D, forming the pattern may further include
forming a first pattern 32 by performing vibrational indentation
patterning in the first direction relative to the substrate, and
forming a second pattern 34 by performing the dynamic
nanoinscribing in the second direction at an angle to the first
direction. In certain aspects, the first direction may be at an
angle of 90.degree. to the second direction and therefore the
directions are orthogonal to one another.
The two-dimensional nanopatterns according to certain aspects of
the present disclosure can be formed by any of the methods
described above. In certain aspects, the two-dimensional
micro-pattern may be a two-dimensional sinusoidal pattern.
In certain aspects, a 2D pattern may by created by forming a first
pattern by performing a first mechanical patterning step selected
from the group consisting of: dynamic nanoinscribing (DNI),
roll-to-roll nanoimprinting (R2RNIL), localized dynamic wrinkling
(LDW), and vibrational indentation patterning (VIP) in a first
direction. A second pattern can be performing by a second
mechanical patterning step selected from the group consisting of:
dynamic nanoinscribing (DNI), roll-to-roll nanoimprinting (R2RNIL),
localized dynamic wrinkling (LDW), and vibrational indentation
patterning (VIP) in a second direction that is at an angle with
respect to the first direction. In certain aspects, the first
direction may be at an angle of 90.degree. to the second direction
and therefore the directions are orthogonal to one another.
The two-dimensional nanopatterning method according to embodiments
of the present disclosure can form two-dimensional nano-patterns by
performing a combination of the dynamic nanoinscribing,
roll-to-roll nanoimprinting, localized dynamic wrinkling, and the
vibrational indentation patterning. Large-area two-dimensional
nanopatterns can be formed easily and quickly. By applying the
two-dimensional nanopatterns, template, and the part that can be
used in various fields such as electronics, photonics, and
bio-engineering can be easily prepared at high production
rates.
In certain aspects, the method of forming a 2D pattern may include
forming a first pattern by performing a first mechanical patterning
step selected from the group consisting of: dynamic nanoinscribing
(DNI), roll-to-roll nanoimprinting (R2RNIL), localized dynamic
wrinkling (LDW), and vibrational indentation patterning (VIP) in a
first direction. A second pattern can then be formed by selecting a
distinct patterning step selected from the group consisting of:
dynamic nanoinscribing (DNI), roll-to-roll nanoimprinting (R2RNIL),
localized dynamic wrinkling (LDW), and vibrational indentation
patterning (VIP) in a second direction at an angle to the first
direction. In certain aspects, the first direction may be at an
angle of 90.degree. to the second direction and therefore the
directions are orthogonal to one another. In this manner, the 2D
pattern is formed by two distinct 1D patterning techniques.
In certain aspects, the materials used by certain patterning
processes to form the first pattern in the first direction, for
example, R2RNIL or DNI, may be UV or thermal setting materials.
Thus, it is advantageous after this first pattern has been formed
to use a second, distinct patterning process to produce the second
pattern, which may desirably be under very different processing
conditions than the first patterning process conditions. By way of
non-limiting example, if the first pattern in a first direction is
done by UV cured R2RNIL, a second pattern in a second direction
would need to be made by DNI, VIP or thermal cured R2RNIL. Also,
for LDW, two layers with different modulus levels are typically
used, therefore if the first layer is done by one of the processes,
in order to use LDW, a second thin top layer having different
properties will need to be created.
FIG. 3 shows micro-patterning using grating-vibrational indentation
patterning in accordance with an embodiment of the present
disclosure. As shown in FIG. 3, a specialized tool is provided that
enables grating-vibrational indentation patterning (Grating
Vibrational Indentation Patterning, G-VIP) to form a periodic
pattern on a moving polymer substrate by applying vertical
vibration of multiple edges spaced apart.
In certain aspects, the present disclosure thus provides a method
of forming a two-dimensional pattern on a substrate. The method
comprises periodically contacting a vibrating tool comprising a
patterned grating edge with a substrate along a first direction in
a grating-vibrational indentation patterning process. In contrast
to the previous VIP methods where the tool had a flat continuous
edge, the edge of the tool is instead a patterned grating edge.
Thus, the patterned grating edge of the tool defines a plurality of
rows and a plurality of interspersed troughs. It should be noted
that the shape of these rows and troughs is shown to be
rectangular, although in alternative variations, other shapes may
be contemplated. In this manner, the periodic contacting of the
patterned grating edge and the substrate creates a two dimensional
array of discontinuous voids in a single-stroke across the surface
of the substrate. In certain variations, the tool is a cleaved hard
mold tool comprising silicon dioxide (SiO.sub.2). The substrate may
be any substrate this is softer than the tool, for example, a
polymeric substrate selected from the group consisting of:
polyethylene terephthalate (PET), polycarbonate (PC), phenol
formaldehyde resins (PF), and perfluoroalkoxy (PFA). The fabricated
polymer patterns may be transferred onto Si wafers using UV-curable
epoxysilicone resin. In this manner, two-dimensional nanopatterns
can be formed by single grating-vibrational indentation patterning
stroke. Therefore, the overall manufacturing process of the
two-dimensional pattern can be formed efficiently.
Because DNI, R2RNIL, LDW and VIP are based on mechanical
deformation and fully capable of period control, the 2D patterns of
various morphologies can be readily obtained through the
combination of DNI and VIP as well as G-VIP on any substrate that
is softer than the tool. Among the many potential applications, the
use of such fabricated 2D patterns has been demonstrated for
colloidal nanoparticle confinement, which can sort and trap various
biological species including bacteria and circulating tumor cells.
The excellent fabrication throughput of the present methods
facilitates the use of multi-dimensional micro/nano-patterns in
many applications that require large areas.
The technology may thus be used for various commercial
nanopattern-based applications, particularly those requiring
large-area and low-cost production, involving displays, flexible
electronics, photonics, and bioengineering solutions, including
microfluidic devices, by way of non-limiting example.
In certain aspects, a period between each row in a plurality of
rows may be greater than or equal to about 50 nm
FIGS. 5A-5D show SEM images of two-dimensional nanopattern formed
by performing dynamic nanoinscribing according to certain aspects
of the present disclosure. FIGS. 5A-5D thus show 2D nanopatterns,
including a first pattern (1.sup.st DNI) and a second pattern
(2.sup.nd DNI), formed via performing two DNI processes in series
along orthogonal directions or at oblique angles. 700 nm period
two-dimensional nanopatterns are formed by dynamic nanoinscribing
with an SiO.sub.2 mold having a 700 nm period (between rows or
peaks). The morphologies of the 2D nanopatterns created by 2D-DNI
can be specifically tailored by changing the substrate material,
applied force, and processing temperature The grating in FIG. 5A is
formed via dynamic nanoinscribing on a soft perfluoroalkoxy
(PFA-Young's modulus E.apprxeq.0.5 GPa) substrate at 80.degree. C.
and with 5N of load or applied force. The nanopattern thus has a
depth of 350 nm. FIG. 5B shows a relatively hard polycarbonate
(PC-Young's modulus E 2.3 GPa) substrate dynamically inscribed at
80.degree. C. with 5N of applied force. A 180 nm deep 2D
nanopattern is thus formed under same temperature and force as in
FIG. 5A. FIG. 5C shows a 200 nm deep 2D nanopattern formed under
same force where force is 5N, but the temperature is increased to
120.degree. C. for same PC substrate as in FIG. 5C. FIG. 5D shows a
PC substrate dynamically inscribed at 80.degree. C., but with
reduced load of only 1N of applied force. The 2D nanopattern thus
only has a depth of 130 nm.
Generally, the first pattern (1.sup.st DNI) formed by the first
dynamic nanoinscribing step can be slightly deformed by the second
pattern (2.sup.nd DNI) formed by the second dynamic nanoinscribing
step. However, because the mold openings (e.g., the troughs or
valleys in the pattern) do not touch the patterned surface during
the second dynamic nanoinscribing step, overall 2D "waffle-like"
patterns emerge, as can be seen in FIGS. 5A-5D.
The profile of the two-dimensional nanopattern can be controlled by
changing the substrate material, force, or temperature. The DNI
pattern profile largely depends on the plastic deformation of a
substrate induced by the mechanical stress from the edge of the
mold under conformal contact. Hence, polymers that have a certain
level of compliance, relatively low modulus, and a reasonable glass
transition temperature (T.sub.g; PFA.about.90.degree. C.,
PC.about.140.degree. C., for example, a T.sub.g of greater than or
equal to about 80.degree. C. to less than or equal to about
150.degree. C.) are best suited as substrates for DNI processing.
The modulation of the mechanical force and the processing
temperature at the mold-substrate contact zone allows control of
the degree of substrate deformation, namely, the final 2D pattern
topology.
FIGS. 6A-6D show SEM images of two-dimensional nanopatterns formed
with the vibrational indentation patterning in accordance with
certain aspects of the present disclosure. All VIP processing
temperatures for forming the patterns are at room temperature and
all DNI processing temperatures are at 120.degree. C. The period
and depth of pattern formed by vibrational indentation patterning
can be controlled by regulating the vibration frequency (f),
substrate feeding speed (V), vibration amplitude (z), and the
mold-substrate gap (g); for the 45.degree.-tilted tool vibration,
the pattern period .lamda. and depth d are given as .lamda.=V/f and
d=z-g, respectively. (See FIG. 2B above).
FIG. 6A shows a two-dimensional vibrational indentation patterning
at a 45.degree. tilted view on polyethylene terephthalate (PET),
where a first direction of VIP is a shallow pass with relatively
low applied pressure, while a second orthogonal direction is a
deeper pass with greater applied pressure. Thus, two consecutive
vibrational indentation patterning steps are conducted in different
directions. The two-dimensional nanopatterns have different depth
per direction, where a first pattern (1.sup.st VIP) is shallow and
a second patter is deep (2.sup.nd VIP) of 5 .mu.m distance. In
addition, the two-dimensional nanopatterns can be formed with 5
.mu.m gap with 50 Hz (3000 rpm) frequency (f) with the substrate
moving speed of 250 .mu.m/s (V). Because a uniform contact between
vibrating mold edge and the substrate is desirable to form a
uniform line pattern, a flexible or soft polymer is preferably
used. The vibrational indentation patterning can quickly and easily
form a two-dimensional nanopatterns by using a high-frequency
vibration.
FIG. 6B shows two-dimensional patterning on polycarbonate (PC),
where the first direction of patterning is done by dynamic
inscribing (DNI) and the second orthogonal direction of patterning
is done by vibrational indentation patterning (VIP). To control the
topology of the final two-dimensional nanopattern the dynamic
nanoinscribing and the vibrational indentation patterning can be
independently controlled.
FIG. 6C is a top view of two-dimensional patterning under different
conditions on PC, where the first direction of patterning is done
by vibrational indentation patterning (VIP) and the second
orthogonal direction of patterning is done by dynamic inscribing
(DNI). A deep high-frequency VIP followed by a shallow DNI step is
shown in FIG. 6C, while the inset shows an SEM of a two-dimensional
pattern formed by a shallow, high-frequency VIP step followed by a
shallow DNI step. The two-dimensional nanopattern shown in FIG. 6C
includes a 3 .mu.m spaced deep first pattern (VIP) formed by
vibrational indentation patterning and a shallow pattern (DNI)
formed by dynamic nanoinscribing with force of 1N.
FIG. 6D is a top view of two-dimensional patterning, where the
first direction of patterning is done by a shallow, low-frequency,
vibrational indentation patterning (VIP) followed by the second
orthogonal direction of patterning of deep dynamic inscribing
(DNI). The two-dimensional nanopattern shown in FIG. 6D thus has a
7 .mu.m spaced apart shallow first pattern (VIP) formed by low
frequency vibrational indentation patterning and a deep pattern
(DNI) formed by dynamic nanoinscribing with a force of 5N.
FIGS. 7A-7B show SEM images of two-dimensional nanopatterns formed
with the grating-vibrational indentation patterning (G-VIP)
techniques where a patterned grating mold edge makes periodic
indentations over the moving substrate to realize two-dimensional
patterns in one stroke according to certain aspects of the present
disclosure. Thus, such a G-VIP process may use a mold like shown in
FIG. 3 in a VIP device like that shown in FIG. 2B. FIG. 7A shows a
G-VIP patterned polycarbonate (PC) substrate, while FIG. 7B shows a
G-VIP perfluoroalkyl (PFA) substrate with directions marked.
FIGS. 7A-7B show the morphology of the pattern can be controlled to
variety of shapes by changing the process conditions and the
substrate material. By adjusting the substrate moving speed under
the same oscillation frequency, 5 .mu.m, spacing pattern is formed
on PC substrate (FIG. 7A), while a 3.5 .mu.m spacing pattern is
formed on PFA substrate (FIG. 7B).
As described above, the templates and components for electronics,
photonics and bio-engineering can be easily and with high
productivity with the two-dimensional nanopatterns formed by
combination of dynamic nanoinscribing and vibrational indentation
patterning. Especially the two-dimensional nanopatterns can be
applied to large area pattern required for biological applications
such as filtration or particle manipulation systems.
FIG. 8A shows a two-dimensional nanopattern having a 700 nm period
void pattern formed with a first dynamic nanoinscribing (DNI)
pattern in a first direction followed by a second DNI pattern in a
second orthogonal direction on a polycarbonate (PC) substrate in
accordance with certain aspects of the present disclosure. The
two-dimensional nanopattern includes complex planar nanostructures
such as a 2D sinusoidal nanovoid pattern. A microvoid or nanovoid
pattern as defined herein is not merely formed by a linear
intersecting grid or mesh pattern, but rather is formed by certain
patterning techniques described herein that create discrete arrays
of open volume voids having at least one curved surface. In certain
aspects, the nanovoids are contiguous with adjacent nanovoids and
connected to one another due to being formed by a continuous
mechanical patterning technique. In certain aspects, each void may
define a curved shaped, for example, a pyramidal shape or a
hemispherical shape, for example, when formed by a DNI-DNI
patterning. In certain variations, the nanovoid pattern has a
sinusoidal shape, as described further below.
As discussed below, the DNI-DNI process leaves certain structures
intact due to the presence of openings in the grating of the mold
structure as it inscribes in a second direction from the first
direction. In other aspects, the voids may be significantly spaced
apart from one another in an array when formed by a G-VIP grating
technique. The volume of each nanovoid will depend upon the period
of the patterning used in each direction and the depth of the
pattern in each direction. In certain aspects, the pattern includes
a plurality of rows defines a first period of greater than or equal
to about 10 nm to less than or equal to about 10 .mu.m in a first
direction, optionally greater than or equal to about 50 nm to less
than or equal to about 1 .mu.m in a first direction, for example,
about 700 nm. The pattern also includes a plurality of rows in a
second direction that defines a second period of greater than or
equal to about 10 nm to less than or equal to about 10 in a second
direction, optionally greater than or equal to about 50 nm to less
than or equal to about 1 .mu.m in a second direction, for example,
about 700 nm. Where the void pattern has at least one period of
greater than or equal to about 1 it may be considered to be a
microvoid, while a period of less than or equal to about 1 .mu.m is
a nanovoid.
A depth of the features or rows may be greater than or equal to
about 100 nm to less than or equal to about 1 for example, about
800 nm deep. It is contemplated that for certain patterning
techniques the periodicity and/or depth between rows can be varied
along the patterned surface, so that different periods or depths
result in different void volumes in different areas of the surface
of the substrate, which may be capable of selectively associating
with different shape and sized micro- and nanospecies. The 2D
sinusoidal void pattern is capable of confining and manipulating
charged micro/nano-scale entities including nanoparticles, lipid
vesicles, cells, such as cancer cells and bacteria.
In certain aspects, the present disclosure provides a microfluidic
device. FIG. 8B shows a schematic of a top view and side view of a
fluidic device 50 including a substrate 60 patterned in accordance
with certain aspects of the present disclosure. In certain aspects,
the microfluidic device 50 comprises a substrate 60 comprising a
surface defining a two-dimensional pattern of nanovoids. By way of
non-limiting example, a DNI-DNI pattern can create two-dimensional
sinusoidal pattern of nanovoids like that in FIG. 8A, which are
particularly suitable for use as a patterned surface in a
microfluidic device, as described further below. In certain
aspects, the surface defining the pattern bears a charge or may
comprise a charged coating. In certain variations, the charged
coating comprises aluminum oxide (Al.sub.2O.sub.3).
The device 50 includes a compartment 62 for holding a fluid. The
substrate 60 is disposed within the compartment 62 such that the
patterned surface contacts the fluid. The fluid may be an ionic
solution that includes the nanospecies distributed therein, and
thus, may form a suspension. The compartment 62 includes an inlet
64 and an outlet 66, so that fluid is introduced to the compartment
62 via the inlet 64 and exits the compartment 62 via the outlet 66.
The compartment 62 optionally comprises at least one transparent
region 68 through which the substrate 60 can be viewed. Two lateral
spacers 70, for example formed of polydimethylsiloxane (PDMS), can
form the lateral walls of the compartment 62. As shown in FIG. 8B,
a microscope 72 can be used to view the substrate 60 within the
compartment through the transparent region 68 in the compartment
62.
The fluidic device 50 is merely exemplary and as shown includes the
compartment 62 that defines a microfluidic cell chamber defined by
two transparent cover slips. One of these cover slips contains the
700 nm pitch nanovoid array fabricated by 2D-DNI, coated with a 10
nm thick Al.sub.2O.sub.3 oxide layer which is positively charged
(surface charge density+2.06 mC/m.sup.2) when immersed in an ionic
solution (10.sup.-4 mol/L KCl). The other cover slip acts as a
transparent region for top-down microscopic characterization. In
certain aspects, the fluid may comprise a plurality of microspecies
or nanospecies, such as nanoparticles. The term "microspecies" is
intended to encompass a variety of different species that have at
least one microscale dimension. The term "nanospecies" is intended
to encompass a variety of different species that have at least one
nanoscale dimension. For example, the microspecies/nanospecies may
be a charged biological species, a charged microparticle, or
charged nanoparticle. Examples of charged biological species may be
selected from the group consisting of: proteins, peptides, nucleic
acids, cells, such as cancer cells, bacteria, viruses, lipid
vesicles, and any combinations thereof. In other aspects, the
nanospecies may include inorganic or polymeric nanoparticles. In
certain aspects, all spatial dimensions of the
nanospecies/nanoparticle component are less than or equal to about
1 .mu.m (1,000 nm).
The term "micro-sized" or "micrometer-sized" as used herein is
generally understood by those of skill in the art to mean that the
component has at least one dimension less than about 500
micrometers (i.e., 0.5 millimeters). As used herein, a
microspecies/microparticle has at least one spatial dimension that
is less than about 100 .mu.m (i.e., 100,000 nm), optionally less
than about 50 .mu.m (i.e., 50,000 nm), optionally less than about
10 .mu.m (i.e., 10,000 nm), and in certain aspects less than or
equal to about 5 .mu.m (i.e., 5,000 nm). In certain aspects, a
microspecies/microparticle has at least one spatial dimension that
is less than or equal to about 1,000 .mu.m, optionally less than or
equal to about 100 .mu.m, optionally less than or equal to about 50
.mu.m, and in certain embodiments, less than or equal to 10 .mu.m.
In certain aspects, all spatial dimensions of the
microspecies/microparticle component are less than or equal to
about 10 .mu.m (1,000 nm).
The term "nano-sized" or "nanometer-sized" as used herein is
generally understood to have at least one dimension less than or
equal to about 1 micrometer (i.e., 1,000 nanometers). Thus, the
nanospecies/nanoparticle has at least one spatial dimension that is
less than about 1 .mu.m, optionally less than or equal to about 750
nm, optionally less than about 500 nm, and in certain aspects, less
than about 200 nm. In certain aspects, all spatial dimensions of
the nanospecies/nanoparticle component are less than or equal to
about 1 .mu.m (1,000 nm).
In certain aspects, the microspecies of the present disclosure have
an average size or diameter of less than or equal to about 10
micrometers, for example, bacteria. In certain aspects, the
nanospecies of the present disclosure have an average size or
diameter of less than or equal to about 1,000 nm. In certain
aspects, the average diameter of the nanospecies may be greater
than or equal to about 20 nm to less than or equal to about 1,000
nm, optionally greater than or equal to about 30 nm to less than or
equal to about 1,000 nm, optionally greater than or equal to about
50 nm to less than or equal to about 1,000 nm, optionally greater
than or equal to about 100 nm to less than or equal to about 1,000
nm, optionally greater than or equal to about 100 nm to less than
or equal to about 900 nm, optionally greater than or equal to about
100 nm to less than or equal to about 800 nm, optionally greater
than or equal to about 100 nm to less than or equal to about 500
nm, greater than or equal to about 100 nm to less than or equal to
about 300 nm, and in certain variations, optionally greater than or
equal to about 2 nm to less than or equal to about 20 nm. Proteins
may have an average size or diameter of greater than or equal to
about 2 nm to less than or equal to about 20 nm.
The microspecies or nanospecies may have a round shape (e.g., a
sphere or spheroid shape) or may have a variety of other shapes,
such as discs, platelets, rods, irregular shapes, and the like.
In certain aspects, the fluid may be a suspension that comprises a
plurality of nanospecies in the form of nanoparticles, for example,
a suspension of negatively charged polystyrene nanoparticles
(surface charge density-1.6 mC/m.sup.2) which can flow into the
fluidic cell (compartment 62 of device 50). A suspension of
nanoparticles (e.g., negatively charged polystyrene nanoparticles
(NPs)) is injected into the cell immersed in a solution (e.g., NaCl
solution), while the microscope 72 monitors and records the motion
of the NPs. At least a portion of the nanospecies is selectively
associated with the surface defining the two-dimensional pattern of
nanovoids, meaning that only a certain population of the
nanospecies is capable of assembling in the nanovoids, for example,
only nanospecies having a certain size, providing size selectivity
and trapping in the nanovoids.
FIG. 8C shows epifluorescence microscopic images of nanoparticles
(e.g., polystyrene nanoparticles) docked in the
Al.sub.2O.sub.3-coated two-dimensional DNI-DNI framework. The inset
in FIG. 8C shows SEM images taken after the sample is dried, where
the enlarged view in the lower-right corner shows three
nanoparticles confined in three grooves in series within the
sinusoidal void nanopattern.
FIG. 8D shows simulation characteristics as a nanoparticle descends
in the z-direction into the nanovoid of a patterned surface
prepared in accordance with certain aspects of the present
disclosure. Such characteristics will be discussed in further
detail below.
Thus, in certain variations, the present disclosure contemplates a
microfluidic device for selective arrangement of nanospecies. The
microfluidic device may include a substrate comprising a surface
defining a two-dimensional sinusoidal pattern of nanovoids. The
microfluidic device comprises a compartment, for example, a
microfluidic compartment, that is capable of containing a fluid
comprising a plurality of microspecies or nanospecies. In certain
aspects, a microfluidic compartment has a volume of less than or
equal to about 100 mL, optionally less than or equal to about 10
mL, optionally less than or equal to about 1 mL, optionally less
than or equal to about 500 .mu.L, optionally less than or equal to
about 400 .mu.L, optionally less than or equal to about 300 .mu.L,
optionally less than or equal to about 200 .mu.L, and in certain
variations, optionally less than or equal to about 100 .mu.L. The
substrate is disposed within the compartment and the surface
contacts the fluid. The compartment includes an inlet and an
outlet, where the fluid is introduced to the compartment via the
inlet and exits the compartment via the outlet. In certain aspects,
the substrate is a polymeric substrate selected from the group
consisting of: polyethylene terephthalate (PET), polycarbonate
(PC), phenol formaldehyde resins (PF), and perfluoroalkoxy
(PFA).
The compartment may include at least one transparent region or wall
through which the substrate can be viewed inside the compartment.
For example, a detector device may thus be positioned on an
opposite side of the transparent region to provide information on
the surface of the substrate. Such a detector device may be a
microscope, in a non-limiting example. Such a transparent region
may also receive external electromagnetic radiation or energy to
active the nanospecies on the surface of the substrate in other
variations.
In certain aspects, the surface has a first charge and the
plurality of nanospecies has a second charge opposite charge to the
first charge, so that the surface attracts the plurality of
nanospecies. The patterned surface may comprise a coating having a
first charge and the plurality of nanospecies has a second charge
opposite charge to the first charge, so that the surface attracts
the plurality of nanospecies. In certain other aspects, the coating
comprises aluminum oxide (Al.sub.2O.sub.3) having a positive charge
and the plurality of nanoparticles comprise polystyrene having a
negative charge.
The two-dimensional pattern of nanovoids, for example, a sinusoidal
pattern of nanovoids, provides size-selective trapping and assembly
of nanospecies therein. In certain variations, the two-dimensional
sinusoidal pattern of nanovoids may have a period of greater than
or equal to about 10 nm to less than or equal to about 1,000
nm.
In certain aspects, the nanospecies may be nanoparticles, where
their unique properties, such as the strong interaction with light,
well-defined surface properties, high catalytic activity and in
sufficiently small particles, their quantum confinement properties
can be exploited. In particular, if particles of a certain size are
placed in the array format, many other applications can be
exploited including photonic crystals, nanoelectronic devices,
optical switches and filters, filtration devices and biological
assays. A prerequisite for these applications using particles
arrays as functional entities is the control and position
selectivity of their arrangement on a surface. Doing so with
standard microfabrication techniques is difficult, and it is often
time-consuming and inefficient to create sparse patterns of small
nanoparticles using subtractive top-down processing. In certain
aspects, the present disclosure provides suitable particle
patterning and assembly methods with low cost and low complexity.
Besides size-selective particle confinement, separation and sorting
are highly desired in various applications such as diagnostics,
chemical and biological analyses, food and chemical processing and
environmental assessment. A number of methods have been reported
for size-selective particle confinement, separation and sorting,
including pinched flow fractionation (PFF), lateral displacement
sorting, hydrodynamic chromatography, electrophoretic deposition
(EPD), dielectrophoresis (DEP) and other active means utilizing
magnetic, optical and acoustic manipulation techniques. But most of
these methods require a continuous driving flow, complicated
streamline and microfluidic channel design and usually only work
for particles with sizes in micrometer range. For submicron-sized
particles, such as nanoparticles, an intrinsic limitation of these
conventional methodologies makes them unavailable. Thus separation
and sorting submicron-sized particles and biological objects with
high throughput has been very challenging.
In comparison, self-assembly from particle-particle interactions
enables the possibility of packaging particles over a large scale.
However, most self-assembly processes lack size-selectivity and the
controllability of the particle arrangements as well as pattern
features. However, directed assembly of particles as provided by
the certain variations of the present disclosure utilizing
particle-substrate interactions allows greater control of the final
particle positions as well as the selectivity. In contrast to
conventional self-assembly, the geometry-induced electrostatic
interaction between charged particles and a nanostructured
substrate in ionic solution enables the directed assembly of
particles, which does not merely fill predefined structures with
randomly dispersed nanoparticles in solution, yet arranges
nanoparticles at positions that are defined by the substrate's
nanostructured geometry and surface charge.
Thus, for a nanovoid patterned substrate fabricated by 2D dynamic
nano-inscribing (DNI) patterning technique, a low-cost and highly
scalable method of trapping and sorting nanoparticles in a
size-selective manner governed by the geometric-induced
electrostatic and entropic interaction between nanoparticles and
the nanovoid surface patterns is provided.
FIGS. 9A-9E show creating a nanostructured 2D void pattern with a
sinusoidal profile on a polymer substrate using the Dynamic
Nano-Inscribing (DNI) technique (as seen in FIG. 9A). To perform
DNI, a well-cleaved, SiO.sub.2 nanograting mold edge containing the
desired pattern is used to inscribe a polycarbonate (PC) substrate
with well-controlled contact, heating, and inscribing speed. This
process is subsequently repeated in the orthogonal direction, and
the deformation of the polymer surface produces the 2D sinusoidal
nanovoid pattern as shown in FIG. 9A. A SiO.sub.2 grating mold with
700 nm-period is used, which produces the nanovoid pattern with 700
nm in period and 800 nm for the void depth. FIG. 9B shows an SEM
image of a side view of the patterned surface of the nanograting
mold with the 700 nm period grating This patterning technique
enables continuous, scalable and high speed production of 2D
nano-patterns on flexible substrates.
FIG. 9C shows a continuously-created 1D grating formed after the
nanograting mold contacts and slides over a polymeric substrate
under conformal contact and localized heating. FIG. 9D shows a 2D
nanovoid pattern formed from a nanograting mold (scale bar 1
.mu.m). FIG. 9D shows a well-defined sinusoidal surface profiles.
FIG. 9E is a perspective view of an SEM of 2D-DNI-fabricated
nanovoid arrays.
Commercially available flexible substrate films like phenol
formaldehyde resins (PF), polycarbonate (PC) and polyethylene
terephthalate (PET) are pre-cleaned before patterning. Details of
DNI processes along with mold preparation and cleaving procedure
are described in Ahn, S. H. et al., "Dynamic nanoinscribing for
continuous and seamless metal and polymer nanogratings," Nano Lett.
9, 4392-4397 (2009) and Ok, J. G. et al, "Continuous fabrication of
scalable 2-dimensional (2D) micro- and nanostructures by sequential
1D mechanical patterning processes," Nanoscale 6, 14636-42 (2014),
the relevant portions of which are incorporated herein by
reference.
All polymer substrates (PET and PC from Tekra Corp.) are used as
purchased and cleaned using IPA followed by nitrogen drying before
the patterning process. To Perform DNI, a well-cleaved SiO.sub.2
nanograting mold containing the desired pattern along the edge is
prepared. The mold edge is brought into contact with the substrate
at a proper angle and force. The mold edge is then slid over the
substrate while maintaining a conformal contact. The polymer
surface is plastically deformed by the nano-features on the mold
edge, leaving behind a well-defined nanograting pattern. This
process is subsequently repeated in the orthogonal direction, which
produces the sinusoidal void pattern as shown in FIGS. 9D-9E. In
DNI, the pattern period is dictated by that of the grating mold and
voids of various sizes and geometry can be inscribed in a
continuous manner at high speed (about 1 m/min or greater). For
instance, a SiO.sub.2 grating mold with 700 nm-period for 2D
nanovoid patterning is used in this example (unless otherwise noted
in the data). Therefore the void patterns can be precisely
inscribed to a certain size, depending on the size of the particle
to be selectively trapped. Furthermore, the morphologies of the
sinusoidal voids created by 2D-DNI can be specifically tailored by
changing the substrate material, applied force, and processing
temperature.
The microfluidic device for nanoparticle confinement is prepared as
follows. A 2D-DNI-patterned PC substrate is coated with a 10
nm-thick Al.sub.2O.sub.3 layer by RF sputtering (Lab 18-2, Kurt J.
Lesker) and put in the microfluidic cell chamber held at a
separation of 1 mm by PDMS spacers between two transparent cover
slips (for example, as described above in FIG. 8B). Fluorescent
labelled (FITC-525 nm) polystyrene nanoparticles are purchased from
Molecular Probes Ltd. and centrifuged and re-aliquoted into
solutions with varying ionic concentrations. This nanoparticle
suspension has an initial volume fraction of 0.1% wt., which is
injected into the compartment/chamber at a fixed flow rate (10
.mu.L/min). As noted above, the 10 nm thick Al.sub.2O.sub.3 oxide
layer is positively charged (surface charge density+2.06
mC/m.sup.2) when immersed in an ionic solution (10.sup.-4 mol/L
KCl), while the polystyrene nanoparticles are negatively charged
(surface charge density-1.6 mC/m.sup.2). The ionic solution
containing NPs is allowed to equilibrate inside the chamber for 15
minutes before microscopic observation.
Richter CCD combined with an Olympus BX-100 fluorescence microscope
is used to image the particles in solution with an exposure time of
30 ms. SEM imaging is performed using a Philips XL30-FEG at the
typical operating voltage of 10-25 kV, after sputtering a thin Au
film nm) to avoid electron charging.
Under the microscope, the dynamics of the nanoparticles in the
microfluidic device system according to certain aspects of the
present disclosure can be visualized. The charged NPs undergo
Brownian motion in solution and experience an electrostatic
attraction when they are in the vicinity of the oppositely charged
2D-DNI patterned surface (i.e., within the Debye screening length).
Localization and assembly of fluorescently labelled 500 nm diameter
polystyrene particles in the patterned voids can be directly
visualized. The particle size and surface charge density appear to
control the trapping behavior.
FIGS. 10A-10C show the microscope images of 500 nm PS nanoparticles
trapped on the substrates with different surface conditions. In the
absence of the nanovoid pattern on the substrate, only a few
particles are randomly adsorbed on the surface, even in the case
when surface charges are presented by the Al.sub.2O.sub.3 layer. In
contrast, in the presence of the patterned surface with the oxide
layer, much greater amounts of particles are trapped onto the
substrate. Moreover, as seen in the zoomed-in image (and verified
by SEM image) in FIG. 10C, almost all trapped particles are well
confined inside the nanovoids, and have been assembled into the
pre-defined pattern on the substrate. The trapping is stable, even
without any direct chemical linkage. The confined particles adhere
to the surface strongly and cannot be removed by rinsing the
channel with DI water. Only by using stronger physical force, e.g.
placing the substrate in an ultrasonic bath, can most of the
particles be dislodged from the surface.
In order to improve the trapping efficiency and particle pattern
quality, the particle concentration effect on the void pattern fill
ratio is also studied. As this process is diffusion limited and no
external stimuli is applied, increasing the particle concentration
increases the fill ratio to a certain degree and further increasing
the particle concentration beyond 0.01M did not appreciably
increase the fill ratio, as shown in FIG. 10D. The fill ratio is
saturated around 50%. This can be possibly explained due to the
electrostatic repulsion from the particles already confined on the
surface. Thus by increasing the spacing between the nanovoids or
increasing the attractive particle-substrate interaction, such as
by increasing the nanovoid surface charge density, the fill ratio
can be enhanced as well as the pattern quality.
Size-selectivity is also demonstrated on the 2D nanovoid patterned
surfaces used in a fluidic device. While the 500 nm size particles
trapped in a similarly sized void could be expected, an equally
interesting occurrence is whether nanoparticles with other sizes
could also be trapped in these voids. Therefore experiments are
conducted with a fixed void size testing three different particle
sizes (200 nm, 500 nm, 1000 nm) to evaluate the trapping behavior.
Under similar conditions and at the same mentioned flow rate, only
particles of 500 nm diameter appear to be confined in the voids
(FIGS. 11B and 11E). In the case of 200 nm particles, some
non-specific adsorption is observed but no appreciable confinement
in the voids (FIGS. 11A and 11D). Similar results are obtained when
testing 1 .mu.m particles (FIGS. 11C and 11F).
These results indicate the size-selective nature of this method,
which facilitates submicron-sized particle separation and sorting
based on their size and surface charges. To understand this
size-selective behavior, this system is modeled and the interaction
between the charged particles and the charged void surface
simulated using finite element analysis (FEA) method in COMSOL
Multiphysics. The free energies for this system is calculated based
on mean field Poisson-Boltzmann (PB) theory and analyzed in detail
the electrostatic and entropic contributions as a function of
particle position above the patterned structure.
The electrostatic potential contributed by both surface charges and
ions can be calculated by the dimensionless PB equation,
.gradient..sup.2.psi.=.kappa..sup.2 sin h(.psi.) (1) where
.psi..times..times..phi..times. ##EQU00001## is the dimensionless
electrostatic potential,
.kappa..times..times..times..times..times. ##EQU00002## and
.kappa..sup.-1 defines the "Debye length" of the electrical double
layers (EDLs).
Fixed surface charge is assumed at both particle surface and the
surface of the void structures. The boundary conditions for the
potential are defined by the surface charge densities:
.gradient..psi..sigma..times..times. ##EQU00003##
These equations are numerically solved using COMSOL Multiphysics,
and next the free energy of the system is calculated by taking into
account both the energetic and entropic contributions as a function
of particle position above the patterned structure. The free energy
of a charge distribution may be analyzed in terms of its
electrostatic potential energy and the configurational entropy of
the ions and solvent in the electrolyte. The electrostatic energy
of the system is given by:
.times..intg..times..times..times. ##EQU00004##
The entropy change of the system is given by:
.DELTA..times..times..times..intg..times..times..times..function..times..-
psi..times..times..function..times..psi..function..times..psi..times..time-
s. ##EQU00005##
The integration volumes in both equations are the whole simulation
system comprising the charged particle, ions and the surface of the
nanovoids. The system's free energy is then obtained:
F=U.sub.es-T.DELTA.S (4)
So for the present nanopatterned void systems, the free energy can
be expressed as:
.intg..times..times..times..times..times..times..function..psi..times..ti-
mes..times..times..psi..times..times..psi..times..times.
##EQU00006##
FIGS. 12A-12E show the calculated energy change of the system, when
particles with different size approach the bottom of the void in
z-direction. In FIGS. 12A-12C, the geometry of the particles at the
lowest positions in the voids for 200 nm (FIG. 12A), 500 nm (FIG.
12B), and 1 .mu.m (FIG. 12C) particles are shown. FIGS. 12D-12F
show calculated energy change of the system, when particles are
approaching the bottom of the void in z-direction for 200 nm (FIG.
12D), 500 nm (FIG. 12E) and 1 .mu.m (FIG. 12F) diameter particles
respectively.
Though from a purely electrostatic energy standpoint, there exists
a counterintuitive energetic barrier preventing the particles
reaching the bottom of the voids, which is due to the high E field
as well as the stored electrostatic energy between the particle and
the substrate surface when they get close that depletes the initial
screening ions in the EDLs, the free energy of the system that
governs the final net force and potential experienced by the
particles shows a clearly attractive interaction between the
particles and the voids. The appearance of electrostatic energy
barrier can be better understood by considering two parallel
charged surfaces. The free energy of the two surfaces follows the
same behavior as the particle-void system. The attractive
interaction governed by the free energy of the system makes the
void behave like a trap and clearly for the 500 nm particle, this
trap has the deepest potential well and strongest confinement as
compared to that for the 200 nm and 1 .mu.m diameter particles.
These results perfectly explain that the size-selectivity observed
in the experiment is due to the free energy potential well for
particles with sizes that appropriately fits the void.
It is instructive to examine the different roles of electrostatic
and entropic contributions to the trapping process. The
electrostatic interaction appears to be responsible for attracting
the particles toward the void surface, but when the surfaces of the
particle and the void get close, the EDLs of the two oppositely
charged surfaces overlap, so the surrounding cations and anions are
depleted in the EDL overlapping region, which weakens the screening
of surface charges and thus increases the stored electrostatic
energy between these two surfaces. However as the particle
approaches the nanovoid surface, some ions from the overlapped EDL
region are displaced to the free space above, thus increasing the
entropy of the system and leading to strong confinement force.
Thus, in the nanovoid systems according to certain aspects of the
present disclosure, the entropic energy contributes much more to
the final potential well and dominates the size-selective
confinement as is shown in FIGS. 12D-12F. And a better geometric
fit of the particle and the void will displace larger amount of
ions as the gap between the two surfaces closes in, and therefore
causes higher increase in entropy, which leads to deeper free
energy well. Similar ion depletion process and the appearance of
electrostatic energy barrier as well as free energy wells can also
be observed in a simpler system of two oppositely charged parallel
surfaces.
To verify this explanation, the depth of the free energy potential
well experienced by the particles is calculated when they are at
the lowest positions in the voids for particles of different sizes
from 100 nm to 1 .mu.m. The areas of overlapping EDLs between the
particles and the structures are also calculated. As is shown in
FIGS. 13A-13B, the depth of the potential well shows direct
correlation with the EDLs overlapping areas and both of these two
plots show that the nanovoid structure with the current geometry
works best for the 500 nm size particles. These numerical results
provide support that the "best fit" particles have the largest
overlapping areas with the nanovoid structures, which release most
amount of ions and cause the largest entropy change. As a result,
much deeper and sharper energy traps form for the particles of a
particular size. Because the nanovoid geometry is fixed in the
above experiment, only particles of particular size can be
confined, leading to the observed size-selective confinement and
separation of particles. Based on this explanation, the nanovoid
pattern design can be optimized in order to better confine and
extract desired particles with particular size and geometry, all in
a single step process. In certain aspects, a DNI sinusoidal
nanovoid structure may have a hemispherical nanovoid structure,
which has a deeper free energy well for the desired particles and
significantly higher particle size selectivity. Thus a high
resolution selective confinement and separation can be achieved
with a well-designed geometry of the void structure depending on
the nature of the nanoparticles or other nanospecies to be
separated.
In certain aspects, a method for selective arrangement of a
nanospecies on a substrate may include passing a fluid comprising a
nanospecies over a surface of the substrate comprising a
two-dimensional pattern of nanovoids. The fluid may be an ionic
suspension. The nanospecies have a first charge and the surface has
a second charge opposite to the first charge. At least a portion of
the nanospecies in the fluid is trapped and assembled within the
two-dimensional pattern of nanovoids.
In certain aspects, the nanospecies is a charged biological species
or a charged nanoparticle. The charged biological species is
selected from the group consisting of: proteins, peptides, nucleic
acids, cells, viruses, bacteria, and combinations thereof. In other
aspects, the two-dimensional pattern of nanovoids may be
sinusoidal. In certain aspects, each void of the two-dimensional
pattern of nanovoids has a shape selected from a pyramidal shape or
a hemispherical shape. In certain variations, the method may
include introducing a fluid into an inlet of a microfluidic
compartment in which the substrate is disposed, such as the devices
described above. In this manner, the fluid flows over the surface
of the substrate comprising a two-dimensional pattern of nanovoids
in the compartment. After at least a portion of the nanospecies in
the fluid is trapped and assembled within the two-dimensional
pattern of nanovoids, the remaining fluid passes out an exit of the
microfluidic compartment. Such a method provides the ability to
selectively associate a portion of the nanospecies with the
nanovoids, thus providing separations or analytical capability, by
way of non-limiting example.
Based on the two-dimensional patterning techniques and directed
self-assembly of nanoparticles controlled by the geometric-induced
electrostatic and entropic interactions, a single-step, low-cost
methodology is provided to selectively confine, pattern and sort
nanoparticles based upon their size on a flexible substrate with
nanovoid patterns over a large area. This size-selective
confinement is believed to be due to the free energy change of the
system which arises from EDLs overlapping, ionic redistribution and
the associated entropy change. The patterning methodology used here
can enable continuous and high speed production of 2D nano-patterns
on flexible substrates. Application of this selective nanoparticle
confinement method can be extended to scalable localization,
sorting and manipulation of charged biological objects, such as
proteins, lipid vesicles, cancer cells and bacteria.
The foregoing description of the embodiments has been provided for
purposes of illustration and description. It is not intended to be
exhaustive or to limit the disclosure. Individual elements or
features of a particular embodiment are generally not limited to
that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. The same may also be varied in
many ways. Such variations are not to be regarded as a departure
from the disclosure, and all such modifications are intended to be
included within the scope of the disclosure.
* * * * *